Preparation Of BiYO₃-based Photocatalyst And Its Application In The Photocatalytic Water Splitting To Hydrogen^*

Photocatalytic water splitting to hydrogen is consider to be one of the promising strategies to solve the global energy shortage.However,the photocatalytic activity of a single semiconductor is limited due to the severe photoelectron-hole recombination.The construction of the composite catalyst could make photo-electron holes transfered between two semiconductors,which would improve their photocatalytic activities through the synergistic effects between the two semiconductors.In the present paper,two semiconductors with good activity were selected through experiment,then,the BiYO3 was composed with the above photocatalysts and was used in the photocatalytic splitting water to hydrogen.The main content includes the following three aspects:Firstly,organic polymer g-C3N4 was prepared by the high temperature thermal polymerization and the chemical method,using melamine and urea as precursors,respectively.The ZnO,Ce02,and TiO2 were prepared by the precipitation method,the hydrothermal method,and the sol-gel method,respectively.The organic polymer g-C3N4 and the metal oxide described above were used as photocatalysts and applied to the photocatalytic water splitting to hydrogen.The catalyst was characterized by X-ray diffraction(XRD).The results showed that the organic polymer g-C3N4 was obtained from high temperature thermal polymerization and chemical method,however,the crystallinity of the g-C3N4 prepared by the chemical method is poor.The ZnO,CeO2,and TiO2 prepared by the precipitation method,the hydrothermal method and the sol-gel method were single component materials.The photocatalytic activity for water splitting on organic polymer g-C3N4 showed that g-C3N4 prepared by high temperature polymerization use urea as the precursor exhibited the optimal photocatalytic activity;as well as the TiO2 prepared by the sol-gel method exhibited the optimal photocatalytic activity.Secondly,the organic polymer g-C3N4 was composed with BiYO3 according to an electrostatic self-assembly method to synthesize g-C3N4/BiYO3 composite,and used in the photocatalytic hydrogen production from water splitting.The results showed the optimal mass ratio of g-C3N4 to BiYO3 was 2,and there was an interaction between the g-C3N4 and the BiYO3 and formed an interface.Through this interface,photoelectrons could be transferred from the conduction band of g-C3N4 to the conduction band of BiYO3,as well as the photogenerated holes transfer from the valence band of BiYO3 to the valence band of g-C3N4,which could inhibit the recombination of the photo-generated electrons and the holes of each semiconductor.After 4 h,the photocatalytic hydrogen production rates of the composite with mass ratios of 3,2,1,and 0.5 were 41.2,150.6,53.5,and 46.2 ?mol·gcat-1,respectively,while the photocatalytic hydrogen production rates of g-C3N4 and BiYO3 were 17.9 and 23.6 ?mol·gcat-1.All the composite could improve the photocatalytic activity of hydrogen production by the synergistic effect,and the g-C3N4/BiYO3 composite which showed the optimal photocatalytic hydrogen production rate,was 8.4 and 6.4 times higher than that of the g-C3N4 and BiYO3,respectively.Finally,the TiO2 was composed with BiYO3 to synthesize TiO2/BiYO3 composite,and used in the photocatalytic hydrogen production from water splitting.The optimal mass ratio of TiO2 precursor to BiYO3 was 7.The results showed that the BiYO3 acted as the electron and the hole receptors,which could receive photogenerated electrons and holes generated by TiO2,inhibiting the recombination of photogenerated electron holes of TiO2.All the composites exhibited excellent photocatalytic activity in photocatalytic hydrogen production in comparison with TiO2 or BiYO3 alone.After 4 h,the photocatalytic hydrogen production rates of the composite with mass ratios of 3,5,7,and 9 were 155.4,281.8,635.5,and 533.1 ?mol·gcat-1,respectively,while the photocatalytic hydrogen production rates of TiO2 and BiYO3 were 62.2 and 11.1 ?mol·gcat-1.All the composites exhibited excellent photocatalytic activity in photocatalytic hydrogen production in comparison with TiO2 or BiYO3 alone.The TiO2/BiYO3 with a mass ratio of 7 showed the optimal photocatalytic hydrogen production rate,which was 10.3 and 57.7 times higher than that of the TiO2 and BiYO3,respectively.